It is important to understand the basis on which individuals can challenge decisions that affect them, why unelected judges have the power to alter decisions of elected officials, and how public authorities can avoid being vulnerable to successful challenges in future. The key is accountability.

Decisions of public authorities can be challenged in the courts by way of "judicial review": a process by which legislative and executive decisions are reviewed by judges to ensure that they are lawful. The purpose of judicial review is to ensure that public authorities don't go beyond the powers given to them by parliament and that they don't abuse those powers.

In the past courts have often proved deferential for fear of breaching the principle of parliamentary sovereignty. But judges have more recently been active in holding government to account, and have sought to protect fundamental rights in a number of key judgments. Judicial powers were bolstered by the introduction of the Human Rights Act in 2000, which prohibits public authorities from breaching fundamental rights.

If you are looking to challenge a decision, there are some legal hurdles to overcome.

The decision must have been made by a public authority – this is not always obvious, for example, the justice ministry is a public authority, but the Football Association is not.

In addition, you must have "standing"; that is, you must have sufficient interest in the decision – so an individual could challenge a decision to close a local library which she often uses. Sometimes pressure groups can get involved, too, for example, Greenpeace was allowed to challenge a decision relating to a nuclear power station as it had members living in the area.

Finally, decisions have to be challenged promptly and certainly within three months. This rule is strictly enforced as it is seen as necessary to allow public authorities to carry out their functions without ongoing fear of litigation.

Once a review is under way, there are three main grounds on which a decision can be challenged.

• First, on the basis that it was illegal – this usually means that the decision maker has acted beyond the powers granted to it by parliament, or has misunderstood the law.

• Second, because it was irrational – this is difficult to establish, it is not enough to show that a decision was unreasonable, it must be so outrageous that no sensible person who had applied his mind to the question could have arrived at it; a decision could also be disproportionate to the end sought, usually in the context of human rights or European Community law.

• Third, the decision may have been procedurally unfair – a common example is when decision makers fail to carry out an adequate public consultation, as was the case in relation to the Building Schools for the Future decision.

If a decision is successfully challenged (pdf), a court will usually quash it, which makes it void and unenforceable. It can also force an authority to remake the decision, even if that means making the same decision, or prohibit an authority from acting in a particular way. Damages are sometimes available, too.